Guidelines Dietary - Eat For Health

In this way, the Evidence Report was used to develop the graded evidence statements included in these Guidelines.It is important to note that these grades relate to individual diet-disease relationships only – the Guidelines summariseevidence from a number of sources and across a number of health/disease outcomes.Levels of evidence in public health nutritionRandomised controlled trials provide the highest level of evidence regarding the effects of dietary intake on health.However, as with many public health interventions, changing the diets of individuals raises ethical, logistical andeconomic challenges. This is particularly the case in conducting randomised controlled trials to test the effects ofexposure to various types of foods and dietary patterns on the development of lifestyle-related disease.Lifestyle-related diseases generally do not develop in response to short-term dietary changes; however short-termstudies enable biomarkers of disease to be used to evaluate the effects of particular dietary patterns. The questionof how long dietary exposure should occur to demonstrate effects on disease prevention is subject to much debate.While it may be possible to conduct a dietary intervention study for 12 months or more to examine intermediateeffects, there would be many ethical and practical barriers to conducting much longer, or indeed, lifelong, randomisedcontrolled trials with dietary manipulation to examine disease prevention.As a result, evidence in the nutrition literature tends to be based on longer term observational studies, leadingto a majority of Grade C evidence statements, with some reaching Grade B, where several quality studies withminimal risk of bias have been conducted. For shorter term and intermediary effects, particularly when studyingexposure to nutrients and food components rather than dietary patterns, Grade A is possible.The relatively high proportion of evidence statements assessed as Grade C should not be interpreted as suggestinglack of evidence to help guide practice. However, care should still be applied in applying this evidence for specificdiet-disease relationships, particularly at the individual level. 32,39Health professionals and the public can be assured that the process of assessing the scientific evidence providesfor the best possible advice. Only evidence statements graded A, B, or C influenced the development ofthese Guidelines.Grade D evidence statementsGrade D evidence statements occur when the evidence for a food-diet-health relationship is limited, inconclusiveor contradictory. These D-grade relationships were not used to inform the development of Guidelines statements,but can be useful to inform health professionals about the strength of evidence from recent research. The full setof Grade D evidence statements can be found in the Evidence Report 33 and is summarised in Appendix E.Food Modelling System – translating nutrient requirements into dietary patternsThe Food Modelling System was commissioned by the NHMRC between 2008 and 2010. It determines a rangeof combinations of amounts and types of foods that can be consumed to meet nutritional needs with the leastamount of energy for the smallest and least active people within an age and sex group. The modelling applies theNRV Document 8 to meet all NRVs within energy requirements for all groups, including acceptable macronutrientdistribution ranges and suggested dietary targets for all nutrients, with the exception of meeting the high ironrequirements of pregnant girls and women and meeting vitamin D requirements (this is a special case asvitamin D is also produced in the body by the action of sunlight on the skin).The resultant dietary models – Foundation Diets and Total Diets – demonstrate that while nutritional needs aremet through the whole diet and not by single foods, the combination of foods is critical. The models are realisticand flexible in providing information on the serve sizes and minimum recommended number of daily servesrequired for each population group to achieve the required intake of vitamins, minerals and macronutrients.Several processes contributed to the development of this report, including consultation processes arranged byNHMRC and a public consultation of the draft report in April/May 2010, after which the models were finalised.The Food Modelling System informed the revision of the Australian Guide to Healthy Eating and companionresources and was considered together with other sources of evidence to determine the recommendations inthese Guidelines.6EAT FOR HEALTH – australian dietary guidelinesNational Health and Medical Research Council